Most of the current high-capacity switches use a flow that goes from input to switch fabric to output solution, of which the input side performs O/E conversion, forwarding/policy enforcement, and segmentation/queuing/scheduling; switch fabric provides the switching path that connects the input and output ports, and usually includes an arbitrator/scheduler to avoid contention; output side reassembles the packets, performs additional output scheduling, and converts signal from electrical to optical. Such switches face potential issues such as:
1) Electrical switching involves high-speed electrical connection from input/output ports to the switch fabric, such connection has limited connection distance and requires a single chassis or pizza-box type layout, so the switching scale and physical arrangement is limited; and
2) The high-speed electrical connection is usually achieved through a serializer/deserializer (SerDes, or called transceiver), which provides parallel interface to the device's internal processing and serial interface for PCB routing to fabric interface. Such SerDes and the crossbar switch fabric consume a lot of power, in particular when the system has large switching capacity.
Optical burst switching network is one solution for the aforementioned problem, in that the edge router/switch assembles the packets into bursts, setup the path along the network, and then transmit the burst. In one variation, the burst is assembled in the intermediate switching node which performs all-optical switching plus burst assembly function.
Optical label switching is another solution, which uses a short optical label for control and configuring the switching path, while the accompanied data packet or burst is switched all optically. In such switching system, the label is extracted and processed electrically to get the destination and policy information; the switch fabric is configured based on this processing result, and then the data packet/burst is fed into the switch fabric and switched to the destination output port.
Another solution is using external wavelength switch to provide fixed connection from one switch to another, either to increase the switching scale, or to bypass the electrical processing for large volume of traffic.